As generally known, a felt is used to draw water from a wet paper web in the press part of a papermaking machine.
In the press part PP of a papermaking machine shown in FIG. 17, water is removed from a wet paper web WW proceeding between a pair of press rolls PR, using a single felt 10A. In the apparatus shown in FIG. 18, water is removed from a wet paper web WW pinched between two felts 10A in the press part PP. In the apparatus shown in FIG. 19, in which the press part PP comprises a press roll PR and a press shoe PS with a resin belt SB therebetween, water is removed from a wet paper web WW pinched between two felts 10A.
In each of the cases illustrated in FIGS. 17–19, the felt 10A is driven by the rotating press roll or rolls PR, and is compressed in the press part PP.
The general structure of a felt 10A is illustrated in FIG. 20. The felt 10A is endless, and comprises a base body 20A, and a fibrous assembly 30A connected to the base body 20A. The base body, which may be a woven fabric, imparts strength to the felt. The felt 10A enters into the press part PP in contact with a wet paper web, and is compressed as pressure is applied in the press part PP. The felt recovers its pre-compression condition after it moves out of the press part.
Compressibility and recoverability are necessary in a felt because, if the felt were not compressed when entering the press part of the papermaking machine, the wet paper web would be torn as a result of the pressure applied by the press rolls. Moreover, the speed of the felt and the press pressure have both increased as a result of developments in papermaking machinery in recent years. Accordingly, the conditions to which the felts are subject have become more severe, and it has been a challenge to maintain the compression-recovery function, and thereby produce a felt having a satisfactory useful life. Thus, various proposals for structures which may maintain compressibility and recoverability have been made.
One such proposal, described in Japanese Utility Model Registration No. 2514509, is a felt comprising a base fabric woven of thread, and a staple fiber integrated by needle punching with the base fabric. This felt uses fibers which exhibit elasticity as the threads of the base fabric or as the staple fiber. Fibers comprising a polyamide block copolymer which has hard segments composed of polyamide components and soft segments composed of polyether components, may be used as the elastic fibers.
On the other hand, for the purpose of improving compressibility and recoverability, a different felt structure, which does not comprise a base fabric and a staple fiber, has been proposed in Unexamined Japanese Patent Publication No. 504167/2001. In this felt, as shown in FIG. 21, a base body 20A comprises not just a woven fabric 20A1, but also a thermoplastic resin, mesh-shaped, compact sheet 20A2 and a multi-filament reinforcing yarn 20A3, the filaments being surrounded by a synthetic rubber material.
In the felt made in accordance with the first of the above-described proposals, recoverability diminished over repeated passage through the press part, due to the crushing of air voids formed between staple fibers.
In the case of the structure shown in FIG. 21, where an elastic structure, comprising sheet 20A2 and a reinforcement yarn 20A3, is used for improving the sustainability of the felt's thickness, the elastic structure is not compressed easily. As a result, its compression recoverability is not very different from that of the felt shown in FIG. 20, which has no elastic structure.
In view of the above problems, the object of this invention is to provide a felt that exhibits excellent compression recoverability, and the ability to maintain a high level of compression recoverability over a long time. It is also an object of the invention to provide a manufacturing method for such a felt.